Hereditary radiation effects

When ionising radiation acts upon gonads or germ cells, it may cause damage to the genetic material (mutations) which can lead to genetically induced diseases (hereditary defects). These may result in malformations, metabolic disorders, immune deficiencies etc. in the children or grandchildren of exposed individuals or may only become apparent after many generations. Just like cancer, genetically induced diseases do not arise specifically from radiation exposure, but also occur spontaneously or due to other environmental factors and cannot be distinguished by their clinical appearance.

An association between radiation exposure and the occurrence of genetic effects has not been observed in humans to date. The atomic bomb survivors are the largest group of exposed parents. The children of these parents have been registered as study participants and are examined regularly for genetic effects to this day. In comparison with the non-exposed Japanese population, so far no statistically significant increase in the frequency of hereditary diseases has been observed in the children and grandchildren of atomic bomb survivors. For risk estimation, the effects of relatively strong irradiations thus have to be investigated in animal experiments and the effects of low radiation doses on humans, which cannot be recorded statistically up to now, have to be inferred from these results.

Genetic radiation risk

The International Commission on Radiological Protection (ICRP) assumes that the the parental radiation exposure to a single (acute) gonadal dose of 1 gray (Gy) leads to one additional severe disease caused by radiation-induced mutations in 500 births. This genetic risk may last for up to two generations. Chronic radiation exposure may persist over several generations. In this case it is assumed that, with a gonadal dose of 1 Gy one additional mutation, which causes a severe disease, occurs in 100 births.

When estimating the genetic radiation risk, a doubling dose of 1 Gy is assumed in the case of chronic exposure. This means that a dose of 1 Gy doubles the spontaneous frequency of all clinically dominant mutations which is about 2 % per generation. In the case of acute radiation exposure the doubling dose is 0.3 Gy. Among medical diagnostic measures, computed tomography (CT) produces the highest radiation exposure. A CT of the abdomen e.g. causes a gonad dose of about 0.02 Gy. The spontaneous genetic risk, which is at about two to three % for monogenic and chromosomal diseases, increases by about 5 % as a result, that is to a maximum of 3.15 %.